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OUTPUT DEVICES
Present display from the computer system either on a screen similar to a television set or on paper through a printing device. Output can be in several forms such as on disk or tape, by modern, by soft copy output or hardcopy output. Soft copy: This is a temporary output that can be interpreted visually, as on a monitor or screen. Another temporary output device is the speaker box. Hard copy: This is a readable printed copy of computer output, on paper. Monitor ' Computer output is commonly sent to some sort or screen or monitor. This is a television-like display for soft copy output in a computer system. Computers display information in various ways and modes. Resolution (sharpness) of the display, number of characters per line, and the ability to show colours will all vary from mode to mode. Monitors vary in their quality of output, or resolution. The resolution depends on the number of pixels that can be displayed. A monitor can have high, medium or low resolution. Pixels are tiny dots that make up a picture rather like the dots that make up character in a dot matrix printer. A pixel is the smallest area of the screen that can be changed by the computer. High resolution gives clear picture on screen and is typically used for CAD applications. Medium and low- resolution screens show less detail but are cheaper and adequate for many applications. '''Advantages of Monitor ' v Relatively cheap ' v Reliable' ' v Can display text and graphics in a wide range of colours.' ' v They are also quiet and do not waste paper' ' '''Disadvantages of Monitor ' v No permanent copy to keep.' ' v Unsuitable for users with visual problems.' ' ' ' Printers Printers produce hard-copy output on paper. In spite of the introduction of electronic mail, people still seem to prefer output on paper. Printers can be classified by technology or speed. For this purpose we will classify them by technology. Impact printers ' An impact printer is similar to that of a typewriter. This technology forms characters by striking a pin or hammer against an inked ribbon, which presses the desired character on the paper. '''Types of Impact Printers ' ' ' 'Daisy Wheel Printers ' The daisywheel printer uses a wheel as a print head with a character shape performed at the end of each stroke. To print a character, the wheel is rotated and a hammer strikes the backside of the stroke and presses it against the paper. They print at very slow speeds, between 15-75 cps (character per seconds). However, it produces high quality print. Daisy wheel printer cannot print graphics. 'Advantages of Daisywheel Printer ' v High quality print v Can print left and right on one line 'Disadvantages of Daisywheel Printer ' v Extremely slow v Cannot print graphics v Uses only one font at a time 'Dot- Matrix Printer ' The dot-matrix printer forms images one character at a time as the print head moves across the paper. The dot-matrix printer is an impact printer. This printer prints up to 450 cps (character per second). Impact printers touch the paper and can produce carbon copies along with the original. 'Advantages of Dot- Matrix Printer ' v The purchase cost is low and the running costs are very low. v They are robust and can operate in harsh environments. v It is able to print on cut-sheet paper and fanfold paper. v If several sheets of self-carbonating paper are placed into the printer then the impact will produce multiple copies. 'Disadvantages of Dot- Matrix Printer ' v Noisy v Low- resolution v Slow v Poor quality graphics output 'Non Impact printers ' Non- impact printing does not depend on the impact of the print head on paper. The technology forms characters and other images on a surface by means of heat, lasers, photography or inkjets. The printing mechanism makes no physical contact at all with the paper. 'Thermal Printer ' Thermal printers create print images on special heat-sensitive paper by heated wires in a print head. They operate at 160 cps. 'Advantages of Thermal Printers ' v Quiet v Inexpensive 'Disadvantages of Thermal Printers ' v Relatively slow v Expensive to run 'Ink Jet Printers ' Ink jet printers produce images by spraying droplets of electricity charged into ink onto paper, which dries instantly. Most ink-jet printers can produce black-and-white, grayscale and colours outputs. It is much faster than daisywheel and dot-matrix printers. A popular choice for home and school use where small amounts of printing are done and colour printing is only occasionally needed. ' ' 'Advantages of Ink-jet Printers ' v High resolution output v Relatively inexpensive v Produce high quality black and white or colour printing. v Quiet v Faster than impact printers '''Disadvantages of Ink-jet Printers v The printing speed is slow compared to laser printer. v The ink cartridges can be expensive so running costs can be high. Laser Printers ' Laser printers form images much the same way like photocopying machines. This type of printer utilizes a laser beam to produce an image on a drum. The light of the laser alters the electrical charge on the drum wherever it hits. The drum is then rolled through a reservoir of toner, which is picked up by the charged portions of the drum. Finally, the toner is transferred to the paper through a combination of heat and pressure. This is also the way copy machines work. '''Advantages of Laser Printers ' v They are quiet and fast v Produce high quality printouts v Running costs are low because although toner cartridges are expensive to replace, they 'last a long time. ' 'Disadvantages of Laser Printers ' v Colour laser printers are considerably more expensive. v Non- colour laser printers are more expensive than ink-jet printers. 'Plotters ' A plotter is an output device that is used primarily to produce charts, maps, drawings sometimes three dimensional diagrams. There are two main types of plotters: inkjet and electrostatic plotters. Plotters are often used in science and engineering applications for drawing building plans, printed circuit boards and machine parts. 'Advantages of Plotters ' v They are fast and accurate v They can produce far larger printouts than standard printers, up to the size of a small room. 'Disadvantages of Plotters ' v Relatively expensive compared to printers. v Cannot print text document such as letters, reports. ' ' ' ' 'Braille printer ' Braille printer by converting text into the Braille code, this printer produces patterns of raised dots on paper for use by the blind. 'Speakers ' These can play music by the computer from programs or from CD-ROMs as well as spoken output. This is particularly useful for blind users where text or figures can be spoken by the computer. Speech synthesis is used by BT for their directory enquiries service. When the operator has located the number for you the information is given to you through a computer-synthesized voice. The telephone numbers are stored in a database and the computer reads out the number selected by the operator in the form “The number you require is…”. 'Microfiche ' Microfiche is a flat sheet of photographic film containing very small images of the text of a publication. A microfiche reader must be used to read the information. Microfiche is used in libraries, banks and other organizations that keep large volumes of data over long periods of time. Microfiche reduces storage space and makes the portability of data cheaper. '''Advantages of Microfiche v Storage is easy v Cheaper than printing paper v Information is quickly accessible Disadvantages of Microfiche v A microfiche reader is needed to read the microfiche films v Can use only to store large amounts of data Summary table ''' '' '' '' '' 'Soft Copy Output Devices ' '''Soft copy output devices output information to a computer monitor or other temporary output devices i.e. they are temporary output that can be interpreted visually or audibly. Soft copy output devices include: · Monitors · Audio Output · Voice Output · Sound Output · Video Output Audio Output devices- include those devices that output voice or voice-like sounds as well as music and other sounds. These include head phones, speakers and sound cards. Voice Output devices- these convert digital data into speech-like sounds. Speech coding and speech synthesis are two types. These devices are used in telephone number change information systems, in banking, in automobile systems and weather reporting. Sound Output devices- produce digitized sounds ranging from beeps and chirps to music. These sounds are non verbal such as the screeching of a car. Video Output devices- is the output of motion video to be viewed by a computer user. Examples include: § V Videoconferencing § V Virtual Reality § Simulators § Robots § Data Projectors ' '